The present invention relates generally to a method and system for making optical measurements and, more particularly, to a method and system for making optical measurements using optical coherence domain reflectometry.
Optical coherence domain reflectometry (OCDR), a well-known technique, is based on detection of an interference signal and becomes an attractive method for making precision measurements that provide resolution of 10 xcexcm and a dynamic range of more than 100 dB for depth scan up to few mm. Using a high speed linear translation stage, OCDR measurements can be performed at modest high speeds. This method can be used to determine an internal depth image below the surface. OCDR has been developed for imaging of the anterior eye and retina, optical tomography and histology in highly-scattering media, and catheter-endoscope tomography in internal organ systems. The mirror velocity is typically in the range of 30 mm/sec corresponding to a Doppler frequency of 50 kHz. To achieve ultrahigh image acquisition speeds alternative technologies to mirror-translation scanning must be developed.
In U.S. Pat. No. 4,459,570 issued on Oct. 17, 1995 to E. A. Swanson et. al, a method and apparatus for performing various optical measurements is provided utilizing an optical coherence domain refractometer (OCDR). A short coherence optical radiation source applies optical radiation through like optical paths to a sample and an optical reflector. The optical reflector is movable in accordance with a predetermined velocity profile to permit interferometric scanning of the sample, the resulting output having a Doppler shift frequency modulation. This output may be demodulated and detected to obtain desired measurements and other information. Additional information may be obtained by applying radiation from two or more sources at different wavelengths to the sample and reflector and by separately demodulating the resulting outputs before processing. Birefringent information may be obtained by polarizing the optical radiation used, by suitably modifying the polarization in the sample and reference paths and by dividing the output into orthogonal polarization outputs which are separately demodulated before processing.
Another reference of interest is U.S. Pat. No. 5,491,552 issued on Feb. 13, 1996 to A. Knuttel.
It is an object of this invention to provide a new and improved method and system for optically performing high resolution measurements.
It is another object of this invention to provide a new and improved method and system for optically performing high resolution measurements using a diffraction grating.
It is another object of this invention to provide a method and system for obtaining a 2D image of a sample without scanning the sample in the lateral direction.
It is a further object of this invention to provide a method and system for obtaining a 3D image of a sample.
A system for performing selected optical measurements on a sample constructed according to the teachings of certain embodiments of this invention comprises a broad band light source, a beamsplitter for splitting light from said broad band light source into a signal beam and a reference beam, a reference mirror disposed along the path of the reference beam, the sample being disposed along the path of the signal beam, a first lens for bringing the signal beam to focus on said sample, a diffraction grating for receiving reflections from the sample and from the reference mirror and producing therefrom a diffracted beam, the reflections from the sample and the reference mirror being incident on the diffraction grating such that a positive diffraction order from the reflections from one of the sample and reference mirror and a negative diffraction order from the reflections form the other one of the sample and reference mirror are directed along the same path, the number of the two diffraction orders being the same, i.e. both first order or both second order etc., a detector, a second lens for bringing said positive diffraction order and said negative diffraction order which are directed along said same path to focus on said detector, said detector producing an output of said positive diffraction order and said negative diffraction order received, and a computer for processing said output from said detector.
A system for performing selected optical measurements on a sample according to other embodiments of the invention comprises a broad band light source, a first beamsplitter for splitting light from said broad band light source into a signal beam and a reference beam, a reference mirror disposed along the path of the reference beam, the sample being disposed along the path of the signal beam, a first lens for bringing the signal beam to focus on said sample, a diffraction grating for receiving reflections from the reference mirror and producing therefrom a diffracted beam, the reflections from the reference mirror being incident on the diffraction grating such that a diffraction order from the reflections from the reference mirror is directed along a first path, a detector, a second beamsplitter for combining reflections from the sample with the diffraction order along said first path to produce a combined beam, a second lens for bringing said combined beam to focus on said detector, said detector producing an output of said combined beam received, and a computer for processing said output from said detector.
In other versions of the invention a diffraction order from the signal beam is combined with reflections from the reference beam.
A method for performing selected optical measurements on a sample according to certain embodiments of this invention comprises a method for performing selected optical measurements on a sample comprising providing a light source, splitting light form said light source into a signal beam and a reference beam, positioning a reference mirror along thee path of the reference beam, positioning the sample along the path of the signal beam, bringing the signal beam to focus on said sample, positioning a diffraction grating for receiving reflections from the sample and from the reference mirror and producing therefrom a diffracted beam, the reflections from the sample and the reference mirror being incident on the diffraction grating such that a positive diffraction order from the reflections from one of the sample and reference mirror and a negative diffraction order form the reflections from the other one of the sample and reference mirror are directed along the same path, the two diffraction orders being the same number i.e. both first order or both second order etc. providing a detector, bringing said positive diffraction order and said negative diffraction order directed along said same path to focus on said detector, said detector producing an output of said positive diffraction order and said negative diffraction order received, and processing said output from said detector.
A method for performing selected optical measurements on a sample according to other embodiments of the invention comprises providing a light source, splitting light from said light source into a signal beam and a reference beam, positioning a reference mirror along the path of the reference beam, positioning the sample along the path of the signal beam, bringing the signal beam to focus on said sample, positioning a diffraction grating for receiving reflections from the reference mirror and producing therefrom a diffracted beam, the reflections from the reference mirror being incident on the diffraction grating such that a diffraction order form the reflections from the reference mirror is directed along a first path, providing a detector, combining reflections from the sample with the diffraction order along said first path to produce a combined beam bringing said combined beam to focus on said detector, said detector producing an output of said combined beam received, and processing said output form said detector.
In some embodiments, the diffraction grating is stationary and the detector is a one-dimensional linear CCD array while in other embodiments the diffraction grating is moving and the detector is a multichannel diode array whose output is fed into a demodulator.
Various features and advantages will appear from the description to follow. In the description, reference is made to the accompanying drawings which form a part thereof, and in which is shown by way of illustration, specific embodiments for practicing the invention. These embodiments will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing form the scope of the invention. The following detailed description is therefore, not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims.